Combustion Safety Flashcards
7 cards from real HERS practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Combustion Safety flashcards as text
Under BPI combustion safety protocols, what is the maximum acceptable CO level (ppm) in ambient room air before work should be halted and the home evacuated?
Answer: 70 ppm
BPI protocols require halting work and evacuating occupants when ambient CO reaches or exceeds 70 ppm, as this level poses an acute health risk.
What is the purpose of measuring CO in the undiluted flue gas stream rather than in ambient air during a combustion safety test?
Answer: To evaluate combustion quality and detect problems at the source before dilution obscures them
Measuring undiluted flue CO directly evaluates the combustion process quality; ambient readings can be very low even when the appliance is producing dangerous CO concentrations.
A technician replaces an old 80% AFUE furnace with a new 96% AFUE condensing furnace. The old furnace vented through a Type B metal flue. What must be done with the old flue?
Answer: Repurpose it to vent the water heater if it remains atmospheric, and verify draft performance
When a furnace is removed from a shared flue, the remaining appliance (e.g., water heater) must be re-evaluated on the now-oversized flue to ensure adequate draft, as orphaning often causes draft problems.
Which factor is most critical when sizing a combustion air opening into a mechanical room containing atmospherically vented appliances?
Answer: The BTU input of all appliances combined
Combustion air opening sizing is based on the total BTU/hr input of all combustion appliances in the space, per NFPA 54 and other codes.
A gas fireplace insert with a co-axial (pipe-within-pipe) venting system is installed in a tight home. Which statement is most accurate regarding combustion safety?
Answer: It is a sealed-combustion appliance and does not depressurize the CAZ or require indoor combustion air
A co-axial direct-vent gas fireplace insert draws outdoor combustion air through the outer pipe and exhausts through the inner pipe, making it a sealed-combustion system unaffected by indoor pressure.
What condition can cause an induced-draft furnace to produce elevated CO even though it has a powered venting fan?
Answer: A cracked heat exchanger allowing flue gas recirculation
A cracked heat exchanger in an induced-draft furnace can allow exhaust gases to recirculate through the combustion chamber, leading to incomplete combustion and elevated CO in both flue gases and supply air.
When conducting a CAZ depressurization test, a HERS rater records -3 Pa with all exhaust fans running and the house closed up. What is the appropriate next step for an atmospherically vented water heater in the CAZ?
Answer: The result is within acceptable limits; proceed to a spillage test to confirm safe operation
At -3 Pa the CAZ depressurization is within the BPI threshold (typically -5 Pa), so the rater should proceed to a steady-state spillage test to verify the appliance is not spilling under these conditions.